1. Field of the Invention
The present invention relates to a method and system for screening telephone calls addressed to at least one telephone line. The present invention further relates to a communication network comprising such a system.
2. Description of the Related Art
A centralized telephone answering service, in a telephone network, allows a user to activate a voice mailbox wherein a calling party can record voice messages. In particular, when a calling party calls a called party who has activated the telephone answering service, if the called party does not answer the call (for instance, the called party is engaged, or the called party is inaccessible), the call is forwarded to the voice mailbox of the called party. Usually, the calling party receives a voice announcement informing him that the call is being forwarded to the voice mailbox and inviting him to record a voice message in the voice mailbox. Once recorded, the message is stored into the voice mailbox. The called party is thus able to access his own mailbox and listen to the stored message whenever he wants.
In this scenario, when a calling party calls a called party who has subscribed such a centralized telephone answering service, if the called party does not answer the call, the call is forwarded to a Voice Mail Server. The Voice Mail Server is a centralized remote equipment comprising voice mailboxes of a plurality of users who have subscribed the centralized telephone answering service. The voice message of the calling party is then recorded into the voice mailbox of the called party, which is located in such a Voice Mail Server.
Typically, the called party is notified by the Voice Mail Server that a message was recorded into his voice mailbox. In particular, the user is notified by the Voice Mail Server after the calling party has completed the recording of his voice message. Once notified, the called party can listen to the message by dialing a special telephone number allowing it to access its voice mailbox. Once the called party has listened to the message, it can either listen again to the message, or cancel it, or forward it to another user, or simply keep it stored into the voice mailbox without performing any other action.
However, in many cases, it would be desirable for a user to have the opportunity of listening to a message while a calling party is recording it into his voice mailbox and, possibly, retrieving the call before the calling party ends the recording of the voice message. This service is particularly useful when a user wishes to know the identity of the calling party and the call subject before answering.
U.S. Pat. No. 6,310,939 describes a screening and monitoring capability for switch based voice messaging systems that allows a called party to hear the caller and the caller's voice as the caller leaves a message and break in to start a normal telephone discussion if the caller warrants such an action. U.S. Pat. No. 6,310,939 provides for an advanced intelligent network service feature that controls the bridging of the connections to the voice mail and the called party's telephone station.
U.S. Pat. No. 6,639,972 describes a method for screening active voice mail message that enables real time monitoring by a subscriber to the voice mail system of incoming calls. Once the identity of the subscriber is established, the subscriber is presented with the option of screening an incoming message. A subscriber desiring to screen the message responds by activating a predetermined key or sequence of keys to enter a listen-only mode for monitoring of the incoming message. The subscriber may then interrupt the message and take the call, continue listening to the incoming message, or terminate listen-only mode and simply permit the message to be stored for later retrieval.
U.S. Pat. No. 6,031,896 describes a communication system that provides call connection and voice mail service to telephone devices. With this system, a called party has the ability to monitor and control an incoming voice mail message, made by a calling party, which is to be recorded onto a voice mail system. The system includes a switch that connects the incoming calls to the called party and the voice mail system. A voice mail intercept service terminal receives a message to be recorded on the voice mail system and also selectively connects the incoming call to the called party for a two-way communication.
The above patents describe methods and equipments providing screening services which allow a user to listen, through his own terminal equipment (for example a telephone, a mobile phone or an IP Phone) to messages which are intended for the terminal equipment itself.
In the following description and in the claims, “screening a call” will refer to the ability of a user of:                being informed that a calling party is recording a voice message;        optionally listening to at least a portion of the message while it is being recorded in the voice mailbox;        optionally carrying out actions on the call before the calling party completes the recording of the voice message.        
Traditionally, telephone networks are circuit-switched networks, both fixed and mobile. The ensemble of interconnected public circuit-switched fixed telephone networks is referred to as Public Switched Telephone Network or PSTN network. Similarly, the ensemble of interconnected public circuit-switched mobile telephone networks is referred to as Public Land Mobile Network or PLMN network. Typically, a user of a PSTN or PLMN network is provided with a user terminal equipment, which is connected to the network by means of a telephone exchange. More users are connected to the same telephone exchange. PSTN and PLMN networks are further provided with a signalling system; when a calling party makes a call, the signalling system provides telephone exchanges with signalling information, through a suitable signalling protocol. According to signalling information, telephone exchanges configure themselves in order to activate a connection between the calling party and the called party. An example of signalling protocol is the ISDN User Part protocol, or ISUP protocol.
PSTN and PLMN networks are able to support a number of services, such as, for instance, the above mentioned centralized telephone answering service. Presently, providers wishing to create, upgrade and/or modify services provided to their users in a very versatile way, recur to a so called Intelligent Network architecture. It is known that the Intelligent Network architecture is a PSTN/PLMN network architecture allowing to create, upgrade and modify services without substantially modifying telephone exchange hardware/software. The Intelligent Network provides for concentrating service management functions in proper Intelligent Network devices, which are distributed across the network. Such Intelligent Network devices may be either physically separated from the telephone exchanges, or they can be implemented into the telephone exchanges. An Intelligent Network architecture comprises different types of Intelligent Network devices, each type being responsible of carrying out a set of service management operations. Different Intelligent Network devices may communicate e.g. through an Intelligent Network Application Protocol, or INAP protocol.
Recently, telephone services which were traditionally supported by PSTN and PLMN networks may be implemented in packet-switched networks as well. For this purpose, real-time packet transport protocols have been developed, such as the Real-time Transfer Protocol. Besides, signalling protocols have been developed, in order to support a signalling system for telephone traffic in a packet-switched network, such as the Session Initiation Protocol or SIP protocol. For a detailed description of SIP protocol, reference can be made to RFC 3261 “SIP: Session Initiation Protocol” by J. Rosenberg et al., June 2002; to RFC 2976 “The SIP INFO Method”, by S. Donovan, October 2000; and to RFC 3515 “The Session Initiation Protocol (SIP)” by R. Sparks, April 2003.
In a packet-switched network supporting telephone services, each user is provided with a suitable user terminal equipment. For instance, users of Voice over IP service, which is supported by IP based packet-switched networks, are provided with an IP Phone. Such an IP Phone is provided with a voice receiver, a voice transmitter and suitable devices for converting voice signal into IP packets and vice versa. Each terminal user equipment is connected to the packet-switched network providing telephone services by means of a proxy server. Different users are connected to a same proxy server. Each proxy server is responsible for managing telephone service requests coming from users connected to the proxy server. In particular, for each request, the proxy server exchanges signalling information by means of the signalling protocol with other devices of the network. According to signalling information, the request is served by allocating the appropriate resources.